[PATCH] selftests: mm: protection_keys: save/restore nr_hugepages value from launch script

[Muhammad Usama Anjum]

The save/restore of nr_hugepages was added to the test itself by using
the atexit() functionality. But it is broken as parent exits after
creating child. Hence calling the atexit() function early. That's not
it. The child exits after creating its child and so on.

The parent cannot wait to get the termination status for its children as
it'll keep on holding the resources until the new pkey allocation fails.
It is impossible to wait for exits of all the grand and great grand
children. Hence the restoring of nr_hugepages value from parent is
wrong.

Let's save/restore the nr_hugepages settings in the launch script
instead of doing it in the test.

Fixes: c52eb6db7b7d ("selftests: mm: restore settings from only parent process")
Reported-by: Joey Gouly <joey.gouly@xxxxxxx>
Closes: https://lore.kernel.org/all/20240418125250.GA2941398@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx>
---
 tools/testing/selftests/mm/protection_keys.c | 38 --------------------
 tools/testing/selftests/mm/run_vmtests.sh    |  2 ++
 2 files changed, 2 insertions(+), 38 deletions(-)

diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
index 374a308174d2b..48dc151f8fca8 100644
--- a/tools/testing/selftests/mm/protection_keys.c
+++ b/tools/testing/selftests/mm/protection_keys.c
@@ -54,7 +54,6 @@ int test_nr;
 u64 shadow_pkey_reg;
 int dprint_in_signal;
 char dprint_in_signal_buffer[DPRINT_IN_SIGNAL_BUF_SIZE];
-char buf[256];
 
 void cat_into_file(char *str, char *file)
 {
@@ -1745,42 +1744,6 @@ void pkey_setup_shadow(void)
 	shadow_pkey_reg = __read_pkey_reg();
 }
 
-pid_t parent_pid;
-
-void restore_settings_atexit(void)
-{
-	if (parent_pid == getpid())
-		cat_into_file(buf, "/proc/sys/vm/nr_hugepages");
-}
-
-void save_settings(void)
-{
-	int fd;
-	int err;
-
-	if (geteuid())
-		return;
-
-	fd = open("/proc/sys/vm/nr_hugepages", O_RDONLY);
-	if (fd < 0) {
-		fprintf(stderr, "error opening\n");
-		perror("error: ");
-		exit(__LINE__);
-	}
-
-	/* -1 to guarantee leaving the trailing \0 */
-	err = read(fd, buf, sizeof(buf)-1);
-	if (err < 0) {
-		fprintf(stderr, "error reading\n");
-		perror("error: ");
-		exit(__LINE__);
-	}
-
-	parent_pid = getpid();
-	atexit(restore_settings_atexit);
-	close(fd);
-}
-
 int main(void)
 {
 	int nr_iterations = 22;
@@ -1788,7 +1751,6 @@ int main(void)
 
 	srand((unsigned int)time(NULL));
 
-	save_settings();
 	setup_handlers();
 
 	printf("has pkeys: %d\n", pkeys_supported);
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 223c2304f885c..3157204b90476 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -390,6 +390,7 @@ CATEGORY="ksm_numa" run_test ./ksm_tests -N -m 0
 CATEGORY="ksm" run_test ./ksm_functional_tests
 
 # protection_keys tests
+nr_hugepgs=$(cat /proc/sys/vm/nr_hugepages)
 if [ -x ./protection_keys_32 ]
 then
 	CATEGORY="pkey" run_test ./protection_keys_32
@@ -399,6 +400,7 @@ if [ -x ./protection_keys_64 ]
 then
 	CATEGORY="pkey" run_test ./protection_keys_64
 fi
+echo "$nr_hugepgs" > /proc/sys/vm/nr_hugepages
 
 if [ -x ./soft-dirty ]
 then
-- 
2.39.2